The present invention relates to methods and systems for wireless communications. More particularly, the present invention relates to methods and systems for channel selection management in a wireless communication network.
Wireless communications may play an important role in the exchange of audio, video or other information, which may be communicated in the form of data. To extend the coverage of a base station in a wireless communication network, relay stations subordinate to the base station may be provided to forward signals between the base station and a mobile station. However, limitation on transmission capacity of the relay stations may limit throughput of data or amount of data exchanged within a time period. Also, as the mobile station moves within the coverage of an infrastructure station such as the base station or the relay station, it may be necessary to switch its access station from the one infrastructure station to another infrastructure station.
In wireless communications, control information, such as that for allocating wireless communication resources or controlling other aspects of data exchange between two or more stations, may be transmitted together with actual data. In some applications, the need for a base station or a relay station to process or handle the control information, which may be transmitted in the form of a control message, may consume additional resources and further limit the transmission capacity or throughput available for the actual data.
A so-called “transparent relay station (transparent RS)” may therefore be applied to enhance the transmission capacity or the throughput available for the actual data. A transparent RS may refer to an RS that does not transmit its own control information or control message on a broadcast connection when downlink accessing its attached mobile stations. As a result, the transparent RS may reduce the operation and control overhead. Moreover, it may be possible for several infrastructure stations in a wireless communication network such as a multi-hop relaying network to share the same broadcast information such as the control information on synchronization or resources allocation so that a mobile station may communicate with one of the infrastructure stations without initiating any handover or being aware of any change of its access station from one transparent RS to another transparent RS when the mobile station migrates in coverage from one transparent RS to another. However, additional mechanism may be required for maintaining connectivity between the mobile station and one of the infrastructure stations. A so-called channel selection management in, for example, a handover process or the change of an access station from one transparent RS to another, may be necessary in the wireless communication network.
FIG. 1 is a diagram of an exemplary wireless communication network. The wireless communication network may include a base station (BS) 102, a relay station (RS) 104 and a mobile station (MS) 106. The base station 102 may be an access station for the relay station 104 and the mobile station 106, and the relay station 104 may be an access station for the mobile station 106. Specifically, the base station 102 may be configured to transmit base-station data to and receive mobile-station data from the mobile station 106. Furthermore, the base station 102 may be configured to transmit the base-station data to and receive relay-station data from the relay station 104. The base station 102 may also be configured to transmit control information or a control message to the relay station 104 and the mobile station 106. The relay station 104 may be configured for relaying at least a portion of the base-station data, and the mobile station 106 may be configured to receive the base-station data and/or the relay-station data and transmit the mobile station-data. The mobile station 106 may also be configured to receive the control information from the base station 102 without any intermediate relay station such as the relay station 104 for relaying the control information. That is, the relay station 104 is “transparent” to the mobile station 106.
In some examples, the mobile station 106 may be configured to receive the base-station data and transmit the mobile-station data through one or more relay stations. The control information may include one or more resource allocation information, a control message “MAP”, ranging response message “RNG-RSP” and/or a connection identification (CID) assignment, depending on its applications. Additionally, the mobile station 106 may be configured to respond to the control information with an initial ranging code and a ranging request message “RNG-REQ”, depending on its applications.
In some prior art methods, channel selection management may be achieved by maintaining a candidate set of infrastructure stations and selecting an infrastructure station from the candidate set as a next access station for the mobile station before switching the mobile station's access station or performing a handover, either soft handover acquired for better macro-diversity gain or hard handover for seamless switching. Examples of the prior art methods may include U.S. Pat. No. 6,714,788 to Voyer, entitled “Method of Reducing Base Station Overloading,” U.S. Patent Application Publication No. 20060223535 by Das et al, entitled “Hard Handoff Procedure for Dedicated and High Speed Shared Channels,” and U.S. Patent Application Publication No. 20060285520 by Venkitaraman, entitled “Method and Apparatus to Facilitate Handover.” However, these prior art techniques for channel selection management may need periodic monitoring and reporting of scanning results of periodic measurement and evaluation of candidate stations in order to improve transmission capacity or enhance transmission efficiency in some applications. Consequently, in some applications the prior art methods or apparatuses in the examples might not be efficient enough or suitable for performing a seamless handover in a wireless communication based on transparent RSs. Furthermore, a mobile station may not perform a handover request if an access station to which the mobile station may switch is included in the candidate set of infrastructure stations. It may therefore be desirable to have a method or a system for channel selection management to facilitate or enhance handover for a mobile station.